Kinetic Isoconversion Loop Catalysis: A Reactor Operation Mode To Investigate Slow Catalyst Deactivation Processes, with Ni/Al2O3 for the Dry Reforming of Methane

Deactivation of heterogeneous catalysts is an issue of high importance and extensive study. However, under normal isothermal plug flow operation the experimental conditions within the catalyst bed can change dramatically with time as the catalyst deactivates and the concentrations of reactants and products respond. Changes of reaction conditions can have diverse simultaneous effects on the rates of catalytic and homogeneous reactions, leading to a discrepancy between the real rate and the measured rate of catalyst deactivation, and/or can directly affect the rates of individual mechanisms for catalyst deactivation. Here we present a simple approach to investigating long-term changes in catalyst activity, whereby the total flow rate of all feed components is varied in response to changes in activity to maintain a targeted overall conversion. This allows experimental measurements to focus in on quantifiable changes in the catalytically active sites directly without a priori knowledge of the reaction kinetics. The dry reforming of methane reaction with a Ni/Al2O3 catalyst is used here as a case study. Using kinetic isoconversion loop catalysis to deconvolute simultaneous deactivation processes, we show that CO disproportionation is the cause of carbon deposition at 550 degrees C and estimate an apparent activation energy of 160 kJ mol(-1) for a second deactivation mechanism attributed to Ni sintering.